A cross-sectional study with a sample of 420 drug users from Porto Alegre, Rio Grande do Sul State, Brazil, was utilized to assess demographic variables, drug use, and risk behaviors for HIV infection. We used the Brazilian version of the Risk Assessment Battery. Overall HIV seropositivity was 22.6%; 39.3% of the subjects infected were at least 30 years old, and 69.5% were males. In the month prior to the interview, 56.8% of the sample had used marijuana, 43.6% had sniffed cocaine, 17.6% had injected cocaine, and 42.4% had used alcohol on a frequent basis. The variables that continued to be associated with HIV infection after logistic regression were age (30 or older) (OR: 2.89; 95%CI: 1.17-7.12), having less than seven years of schooling (OR: 2.10; 95%CI: 1.02-4.36), having a monthly family income of less than one minimum wage, or approximately U$90 (OR: 2.89; 95%CI: 1.32-6.32), and having injected drugs (OR: 5.18; 95%CI: 1.32-6.32). Seroprevalence in this sample is considered high, particularly since 70.0% of the sample reported no prior drug injection. Variables associated with HIV infection are similar to the national and international literature and agree with the theoretical model of risk behavior proposed by the first author.